Manufacture of bleaching powder



Patented Oct. 5, 1931 umrE-n STATES rarsurorrics JOSEPH WILLIAM MOORE, or RUNCOR-N, n samaam ALFRED LAMBLE, or LIVER- POOL, ENGLAND, assrenons TO IMPERIAL. CHEMICAL. INDUSTRIES LIMITED, or

' LONDON, ENGLAND, A BRITISH Conrail-Y MANUFACTURE or nrlnacnmerownna i in Drawing. Application filed April. 19, 1929, SerialNo. saseaana in Great Britain me a, 19 2s.

, This invention relates to improved means for the manufacture of stabilized bleaching powder by the removal of moisture, the presence ofwhich isknown to be one of the chief causes of instability, especially in tropical countries. The dehydration of bleaching powder as an entirely separate operation,

' using heat from an external source, is described in British Patent specification No. 242,805, and No. 246,000.

Thus it is known that dehydration may be effected by heating the powder in shallow I layers exposed to the atmosphere, or by passing a current of heated air or inert gas in countercurrent over the bleach. 7

*Such a method is expensive because of the heat which has to be supplied to the gas in I order to raise the temperature of the bleaching' powder sufficiently tocause the transfer of water to take place from the bleaching powder to the air, and by reason of extra plant and labour required.

According to the present invention, the

manufacture and all or part of the drying of the bleaching powder are combined in one operation. We have discovered that this can be done by taking advantage of the heat of reaction evolved during the manufacture of the bleaching powder. Preferably we circulate a controlled volume of dilute chlorine through the apparatus during the manufacture of the bleaching powder'the moisture being removed from the efiluent gas (e. g. by

cooling) before it is re-circulated.

In this way, Valuable economies can be efto effect the removal of water. 'ternal source of heat is now unnecessary, the I heat required for the drying of the bleaching powder being practically completely sup- I 1 (1) By eliminating the heating of a large volume of air or inert gas, required by the original process. This volume of air was necessarily large because it has to raise the temperature of the bleaching powder sufficiently Such an execonomizing in plant and labour ,The addi; tional plant or labourformerly required for a separate drying process and the cost of transport I of bleaching powder from the 1 manufacture'to the 'dryingplant are avoided. The combined operation may be effected in anapparatus of the mechanical type, preferably the Moore rotary tube (British PatentNo. 113,457) as impaired stability due to iron contamination from the plant is avoided in this apparatus. I 1 I The tube consists of a long iron cylinder suitably supported at intervals byroller bearings and lined-with glazed earthenware tiles.

It is fixed at an inclination of about 1 in 24:

and is caused to rotate by worm gearing. At

the upperend is fitted a hopper with ribbon feed for, a regular supplyof lime and the finished bleaching powder discharges into a Suitable hopper at the lower'end of the tube.

'A slight suctionis maintained on the apparatus by a fan which drawsthe hot exit gas from the lime feed end, through a series of nearly parallelearthenware pipes, arranged as atmospheric coolers. If required, furthen-cooling may be efiected'by passing-the gas through pipes immersed in artificial cooled brine. The condensed water -is drainedtawayand the dried exit gas, after adjustment of strength withstrong chlorine, is" delivered by thefan to the inlet gas pipe of the tube; Any other suitable method of drying may be used e. g. passage in contact with strong sulphuric acid.

A large predetermined volume of weak chlorine is continuously circulated, and in its passage through the tube, the gas temperature is raised to about 60 C. due to reaction heat evolved, thus producing suitable drying conditions.

We have found that satisfactory dehydration is obtained if, say, 10,000 to 12,000 cubic feet per hour are circulated through the tube producing about 32tons per week of high strength bleaching powder, e. g. containing 37% available chlorine, or thereabout.

The volume of gas used, however, will vary somewhat with its conditions of dryness and type of plant used.

An important feature of the invention conice i 2 "I f 1,826,629

5 when necessary.

7 sists in the circulation of'Wea-k gas, with ad- 7 "justment, of chlorine content, and removaflof water, With thermal control. If desired, the

' inlet gas may be'heatedto assist in'drying By means' ofjithee'herein describedonefstage process asubstantially anhydrous iproductis' .I. obtained which is especiallyzidaptedionflse in tropiealicountries, andis known as 5tropi- 10' ar. l-lbleachiiig powder; 1 ysuch bleaching:

powder contains onlyebout to1%% free 7 p weteryasfcompa-red with about 7% free Water w in ordinary; bleachingipowderr; Tropical;

bleaching powder is a known product, which,

7 i5 howevenxhas always. -'be eni produced fin twovi I I se at ere sb t p fientlpro Y M feseth'e 'pr'gjductis produced s ing l eigt zvg I i as 131 airtim -free waiter hajs ben removed-"from i 7 ing the reactionheingmeintuii ediatisuhstirr H momaehingpowdr; the; tem era u-i-ez(1m 1 il l jf ,7 1 23A one-stage process for producing'su'h- Qq fntiallj anhydrous bleaching; powder dammedu ing thireaetion; I

' 10 Whiohfconsists in-pess ii'igfdiliite chlorine over i 45 g-reeterjthan'1 which conists in passing dilute chlorinefover agitatedliine'rndteriaifand keeping the @1116; rineso dilute;themoisturecontentof thein itfga's so 16W and theteinperiture such that 35 Qub tanti''HY aH" free'noo'isture i's fremoved i r-WitHout'deconipositionof the'bleechingpow 3: A?" oneI-s'ta'gef process jforiii roducihg' I substantially fanhydroue bleaching pondr 1 zi'gitated'iiniematerial;and keepihgithchloe 1* rineis odiluteQQthe-"rfioiStuTe bon'tent ofth'inlt' gus 'so 16w and'lthetemprhtureuchjheta bleaching powder ontai'ningnotfmaterially" 

